1. Technical Field
The present invention relates to an indoor installation type combustion apparatus having housed inside an exterior case: a burner; a combustion box for enclosing a combustion space of air-fuel mixture ejected from the burner; and an exhaust duct through which exhaust gas discharged from the combustion box flows. In this combustion apparatus, as an air supply pipe to supply air into the exterior case from outside, an arrangement has been made that use can be made of both an air supply pipe of double-pipe system in which an exhaust pipe is housed inside the air supply pipe, and an air supply pipe of twin-pipe system in which the air supply pipe is independent of, and separate from, the exhaust pipe.
2. Background Art
In this kind of indoor installation type combustion apparatus, an upper surface of the exterior case has formed therein: a cylindrical exhaust connection port which is in communication with an exhaust duct and which is connectable to an exhaust pipe; a first cylindrical air supply connection port which is connectable to an air supply pipe of double-pipe system and which encloses the exhaust connection port; and a second cylindrical air supply connection port which is connectable to an air supply pipe of twin-pipe system (see, for example, JP-A-2015-183887). In this arrangement, at the stage of delivery, each of the first and the second air supply connection ports is closed by respective lid members. In case the air supply pipe of double-pipe system is used, the air supply pipe is connected to the first air supply connection port in a state in which the lid member closing the first air supply connection port has been removed. On the other hand, in case the air supply pipe of twin-pipe system is used, the air supply pipe is connected to the second air supply connection port in a state in which the lid member closing the second air supply connection port has been removed
By the way, since the air to be supplied through the air supply pipe will sometimes contain foreign matters, it is necessary to prevent the foreign matters from entering the exterior case. As a solution, at that outlet portion of each of the first and the second air supply connection ports which is in communication with the inside of the exterior case, a supply-air filter (i.e., a filter for filtering air to be supplied) is respectively mounted. According to this solution, however, two kinds of supply-air filters are necessary for the first air supply connection port and for the second air supply connection port, thereby resulting in an increase in cost.